Rate Constants for Reactions in Gas-phase Hydrocarbon Oxidation

Rate Constants for Reactions in Gas-phase Hydrocarbon Oxidation 

Atmospheric chemistry demands have given a nuuked stimulus to studies of reactions of 0 atoms and OH- radicals with atmospheric substrates at about room temperature and below. Reactions of O atoms with alkenes and aromatics are important in photochemical smog formation and control. Rate constants, and in many cases Arrhenius parameters, are available for a variety of -O atom reactions with alkenes, alkynes, aromatics, unsaturated aldehydes, alkanes, - and carbonyl compounds. In general, the rate constants refer to the ovoall process  

Arrhenius parameters for O + SO2 + M suggest that the reaction is not an important path for the conversion of SO2 into SO3 in the troposphere, and Westenberg and de Haas report that O + SO3 is a third-order reaction up to pressures of 7 nunHg and follows the mechanism  

Of late, considerably more attention has been paid to the accuracy and precision of gas-phase kinetic techniques. With the development of direct methods of 

AB olefinic compound ABO carbonyl compound OR = 0-ring compound R, AB contain smaller number of carbon atoms than R. Reactions for specific compounds are indicated by attaching an appropriate letter. Broken arrows in reactions (SA), (SB), and (SQ indicate overall processes. 

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R.W. Walker, A Critical Survey of Rate Constants for Reactions in Gas-Phase Hydrocarbon Oxidation, Specialist Periodical Reports (The Chemical Society, London (1975) p. 161. 

Rate Constants for Reactions in Gas-phase Hydrocarbon Oxidation 4 Hie Initiation Process... 

Oxidation rate constant k, for gas-phase second order rate constants, koe for reaction with OH radical, k os with NO3 radical and koj with O3 or as indicated, data at other temperatures see reference photooxidation ty, = 267 d-64.6 yr in water, based on measured rate constant for the reaction with OH radical (Anbar Neta 1967 Dorfman Adams 1973 selected, Howard et al. 1991) photooxidation ty, = 0.24-2.4 h in air for the gas-phase reaction with OH radical, based on the rate of disappearance of hydrocarbon due to reaction with OH radical (Darnall et al. 1976) kgjj = (7.7 1.1) X 10 cm molecule S at 295 K in air (Wiedermann Zetzsch 1982 quoted, Atkinson 1985)... 

Traylor and Russell (30) have shown recently that similar reactions for the cumyloxy radical are important in cumene oxidation at 60 °C., and Hendry (12) has provided some quantitative data. At low concentrations of hydrocarbon, Reaction 9 is favored over Reaction 7 (propagation by tert-BuO ), and significant numbers of methyl radicals are formed and converted to Me02 radicals. Chain termination thus shifts from the slow termination by 2 tert-Bu02 (Reaction 6) to Reaction 10, which has a rate constant several hundredfold larger (21). The apparent order of the oxidation in isobutane is then 3/2 a similar relation applies to gas-phase oxidations and is discussed there. 

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